Japanese Patent No. 4838122 (Patent Literature 1) is one of background arts in the technical field. The patent publication describes “an optical apparatus comprising: a second optical device which focuses a radiation light ray on a second focused light ray at a second incidence angle corresponding to the vertical direction or substantially the vertical direction relative to an illuminated area on a surface of a sample and the second incidence angle of which is different from a first incidence angle; an elongated reflection surface that reflects a radiation ray in the light ray focused by the second optical device to the illuminated area on the surface of the sample; a first detector array; and a light-condensing optical device which condenses the radiation ray generated from the first and/or second focused light rays and scattered or reflected from a first line and/or the illuminated area on the surface of the sample, which focuses the radiation ray condensed from parts of the line and/or the illuminated area on a corresponding detector in the first array, and which blocks the radiation ray in the light ray that is focused by the second optical device and that is mirror-reflected on the illuminated area on the surface of the sample from reaching the first detector array by using the elongated reflection surface” (claim 1).